1. Field of the Invention
The invention is in the field of the patterning of thin metal layers primarily for use in the production of solid state electronic devices.
2. Brief Description of the Prior Art
The production of both discrete and integrated solid state circuit devices often involves the etching of thin films of reactive metals in contact with more noble metals. For example, a common metallic contact to a silicon device consists of superposed layers of titanium, platinum or palladium and gold. When such layers are etched to define their ultimate shape, a common problem is accelerated attack of the reactive metal layer (titanium), near the point of contact with the more noble metal. This undercutting of overlying layers is usually enhanced by the existance of an electrolytic couple at the contact. This has typically required close monitoring of etching and removal of the etched devices immediately after etching is complete. It is also one factor which tends to place a minimum size limit or realizable conductor patterns.
In a related area of device processing, it is sometimes necessary to etch masked oxide layers on devices which already possess multilayer metallic contacts as described above. An etchant (U.S. Pat. No. 3,860,464, issued Jan. 14, 1975) developed to preferentially etch oxide layers while leaving reactive metal layers relatively undisturbed, involves the use of a tetrazolium salt as a reactive cathodic inhibitor and buffered HF as the etching agent.